The history
From stones that pull iron to compass needles, electromagnets, MRI scanners and neodymium magnets.
People have known for thousands of years that some stones pull iron and that a magnetised needle points north. Gilbert showed in 1600 that the Earth itself is a magnet. In 1820 Ørsted found that electric currents make magnetism, and within a few years came the electric motor and the electromagnet. Since then magnets have gone into every motor, speaker, hard drive and hospital scanner, and observatories from Colaba to Göttingen keep watch on the Earth's own field.
1088
Compass needle described
Shen Kuo, China
1269
Magnet poles named; broken magnet makes two
Petrus Peregrinus, France
1600
The Earth shown to be a magnet
William Gilbert, England
1820
Electric current found to make magnetism
Hans Christian Ørsted, Denmark
1821
First electric motor
Michael Faraday, England
1825
First electromagnet
William Sturgeon, England
1841
Magnetic observatory in India
Colaba, Bombay
1960
Tesla adopted as the SI unit of field
CGPM, Paris
1973
First MRI image
Paul Lauterbur, USA
1982
Neodymium–iron–boron magnet
Masato Sagawa, Japan
600 BCE – 1200
Lodestone pulls iron in Greece and China, and Chinese scholars and sailors turn a magnetised needle into a compass.
600 BCE
c. 600 BCE
Later Greek writers, starting with Aristotle, say that Thales noticed lodestone, a natural magnetic rock, pulls on iron. He is said to have thought the stone had a soul. The story is second-hand, but lodestone was well known in the ancient world, in Greece, China and India.
Why it mattered. It is the oldest story we have of someone wondering why magnets pull.
80
c. 1st century CE
Wang Chong's book Lunheng mentions a 'south-pointer' that comes to rest pointing south. Many historians read it as a lodestone spoon spun on a bronze plate, used for divination rather than travel. Others doubt such a spoon ever existed.
Why it mattered. If the reading is right, it is the first known magnetic direction-finder.
1088
In his Dream Pool Essays, Shen Kuo describes rubbing a needle on lodestone and hanging it from a single silk thread so it points south. He also noted that it does not point exactly south, but a little to the east: the first record of magnetic declination.
Why it mattered. It is the earliest clear description of a compass needle, and of the gap between magnetic and true north.
1117
c. 1100 (written 1117)
Zhu Yu's Pingzhou Table Talks, written in 1117 about the years around 1100, says that ship pilots steered by the stars at night and the Sun by day, and in dark weather looked at the south-pointing needle. The compass reached Europe and the Islamic world within about a century.
Why it mattered. It is the first written record of a compass used for navigation at sea.
1269 – 1860
Poles are named, Gilbert shows the Earth is a magnet, and observatories from Göttingen to Colaba measure its field.
1269
In a letter written during a siege, the French scholar Peter Peregrinus named the two ends of a magnet its poles, showed that like poles repel and unlike attract, and noted that breaking a magnet gives two magnets, each with both poles.
Why it mattered. It was the first careful experimental account of magnets in Europe, and it busts a myth still told today.
1600
Gilbert, doctor to Queen Elizabeth I, spent years testing magnets and published De Magnete. With a small magnetised sphere, a 'terrella', he showed that a compass behaves on it just as on the Earth, dipping near the poles. His conclusion: the Earth itself is a magnet.
Why it mattered. It explained why compasses work and made magnetism a subject for experiments rather than legends.
1785
Using a sensitive twisting balance, Coulomb measured the force between the poles of long magnetised needles and found it falls with the square of the distance, the same rule he found for electric charges.
Why it mattered. It gave magnetism its first mathematical law of force, the pole model this box still uses to draw field lines.
1832
Gauss worked out how to measure the strength of the Earth's field in absolute units, using a swinging magnet and a fixed one. With Wilhelm Weber he set up a network of observatories to record the field at the same moments. The old unit of field, the gauss (1/10,000 of a tesla), is named after him.
Why it mattered. It turned the Earth's field into something you could measure and compare around the world.
1841
Regular magnetic observations began at Colaba in Bombay in 1841. In 1904 electric trams began to disturb the readings, so the observatory moved across the harbour to Alibag, where it still runs. Its first Indian director, Nanabhoy Moos, published two huge volumes of its records in 1910.
Why it mattered. Colaba–Alibag is one of the world's longest-running magnetic observatories.
1859
1–2 September 1859
After Richard Carrington saw a brilliant flare on the Sun, the biggest magnetic storm on record hit the Earth. Colaba's hand-read instruments saw the horizontal field drop by about 1,600 nanotesla, far more than in any storm since, and aurora were seen close to the tropics.
Why it mattered. Colaba's readings are among the best measurements of how strong a solar storm can be.
1820 – 1865
Ørsted's swinging needle leads to Ampère's currents, Faraday's motor, Sturgeon's electromagnet and Maxwell's equations.
1820
21 July 1820
Ørsted saw a compass needle swing when current flowed in a wire above it, reportedly first during a lecture in the spring of 1820. He published the result in a short Latin paper that summer. The needle turned across the wire, showing the field goes round it.
Why it mattered. It joined electricity and magnetism for the first time and set off a burst of discoveries within months.
1820
September 1820
Within weeks of hearing of Ørsted's result, Ampère showed that two parallel wires attract when their currents flow the same way and repel when opposite. He suggested that all magnetism comes from tiny circulating currents. The unit of current, the ampere, is named after him.
Why it mattered. It showed that magnets and coils of current are the same kind of thing.
1821
3–4 September 1821
Faraday hung a wire so its end dipped into a bowl of mercury round a standing magnet. When current flowed, the wire swept round and round the magnet. It was the first device to turn electric current into continuous motion.
Why it mattered. Every electric motor, from a mixer grinder to an electric car, grows from this experiment.
1825
Sturgeon varnished a horseshoe of iron, wound about 18 turns of bare copper wire round it and connected a single battery cell. The 200 g magnet held up about 4 kg of iron, and let go the moment the current stopped. The Society of Arts gave him a silver medal.
Why it mattered. It was the first magnet you could switch on and off, the ancestor of cranes, relays, bells and MRI magnets.
1865
Maxwell gathered everything known about electricity and magnetism into one set of equations. They predicted waves of electric and magnetic field travelling at the speed of light, and he concluded that light is one of them.
Why it mattered. It unified electricity, magnetism and light, and led to radio, microwaves and MRI.
1895 – 1933
Curie, Weiss and others find why iron is magnetic, why heat stops it, and that the Earth's field flips.
1895
For his doctoral thesis Pierre Curie measured how magnetism changes with temperature. He found that iron and other ferromagnets lose their strong magnetism above a certain temperature, now called the Curie point: 770 °C for iron.
Why it mattered. It showed that magnetism depends on the order of atoms, which heat can scramble.
1906
Brunhes found volcanic rocks magnetised in the opposite direction to today's field. In 1929 Motonori Matuyama in Japan showed such reversed rocks come from a particular age. Together they revealed that the Earth's field flips; the last full reversal was about 780,000 years ago.
Why it mattered. It showed the Earth's magnet is not fixed, and later helped prove that the sea floor spreads.
1907
Weiss proposed that inside iron a strong internal 'molecular field' lines up the atomic magnets in small regions, now called domains. An unmagnetised nail has its domains pointing every which way; a magnet nearby lines them up.
Why it mattered. It explained why iron can be magnetised and demagnetised, and why it stops at the Curie point.
1933
Meissner and Ochsenfeld found that a metal cooled into its superconducting state expels a magnetic field from inside itself. Superconductivity itself had been found by Heike Kamerlingh Onnes in 1911. Today superconducting coils make MRI fields, and magnets can float above cold superconductors.
Why it mattered. It showed superconductors are more than perfect wires: they are also near-perfect magnetic shields.
1960 – 2024
The tesla is named, MRI scanners image the body, and neodymium magnets shrink motors, speakers and drives.
1960
The new International System of Units named the unit of magnetic flux density after Nikola Tesla, the inventor of the rotating-field induction motor. One tesla is a strong field: 20,000 times the Earth's.
Why it mattered. It gave the whole world one unit for field strength, from microtesla compasses to 3 T scanners.
1971
Damadian reported that the nuclear magnetic resonance signal of some tumours fades more slowly than that of healthy tissue, and proposed using it to find cancer. On 3 July 1977 his team made the first scan of a whole human body with their magnet, 'Indomitable'.
Why it mattered. It was the first push to use magnetic resonance in medicine.
1973
Lauterbur added a gentle slope, or gradient, to the magnetic field, so that each place in the sample answered at a slightly different frequency. From the answers he built the first magnetic resonance image, of two tubes of water. Mansfield in Nottingham made the method fast. They shared the 2003 Nobel Prize.
Why it mattered. It is the basis of every MRI scan today, made in fields of 1.5 to 3 T.
1982
Sagawa combined neodymium, iron and boron into Nd₂Fe₁₄B, the strongest permanent magnet ever made. He announced it in 1983; John Croat at General Motors found the same compound independently. Mass production followed within three years.
Why it mattered. Neodymium magnets made small, strong motors, headphones, hard drives and electric cars possible.
2024
10–11 May 2024
The strongest magnetic storm in two decades pushed the aurora so far south that all-sky cameras at the Indian Astronomical Observatory in Hanle recorded a red glow over the Himalaya. Scientists in Bengaluru later traced it to several merging eruptions from the Sun.
Why it mattered. It was a reminder that the Earth's magnetic shield is always being tested by the Sun.
By the numbers
The maximum energy product of leading magnet materials, a measure of how much magnetic energy a magnet can store in each cubic metre. Values are typical for each material.
Did you know?
The Earth's field is only 25 to 65 microtesla, yet a compass needle a few grams in weight lines up with it.
A hospital MRI scanner at 3 T is about 60,000 times stronger than the Earth's field, and its coil needs no power to keep the field going.
Break a magnet into as many pieces as you like and every piece has its own north and south pole. No lone pole has ever been found.
Iron stops being magnetic at 770 °C. Neodymium magnets give up much sooner, at about 310 °C.
The magnetic observatory at Colaba had to move to Alibag in 1904 because Bombay's new electric trams upset its instruments.
The people
c. 624 – c. 546 BCE · Philosopher · Greece
Said by later writers to have noticed that lodestone attracts iron.
1031 – 1095 · Scholar and statesman · China
Described the magnetised compass needle and magnetic declination in 1088.
fl. 1269 · Scholar and engineer · France
Named the poles and showed that a broken magnet makes two magnets.
1544 – 1603 · Physician and natural philosopher · England
Showed with a model sphere that the Earth is a magnet, in De Magnete (1600).
1777 – 1851 · Physicist and chemist · Denmark
Found in 1820 that an electric current deflects a compass needle.
1775 – 1836 · Physicist and mathematician · France
Showed that currents attract and repel; the unit of current is named after him.
1791 – 1867 · Physicist and chemist · England
Built the first electric motor in 1821 and later discovered induction (see FaradayClear).
1783 – 1850 · Physicist and lecturer · England
Made the first electromagnet in 1825.
1777 – 1855 · Mathematician and physicist · Germany
Measured the Earth's field in absolute units and organised a network of observatories.
1859 – 1936 · Physicist and observatory director · India
First Indian director of the Colaba Observatory; moved it to Alibag and published its long records.
1831 – 1879 · Physicist · Scotland
Wrote the equations that unite electricity, magnetism and light.
1859 – 1906 · Physicist · France
Found that iron loses its magnetism above a critical temperature, the Curie point.
1865 – 1940 · Physicist · France
Explained ferromagnetism with a molecular field and magnetic domains.
1929 – 2007 · Chemist · USA
Made the first magnetic resonance image in 1973; Nobel Prize 2003.
born 1943 · Materials scientist · Japan
Invented the neodymium–iron–boron magnet in 1982.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
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